The present invention relates to the field of semiconductor devices and their manufacture. More specifically, in one embodiment, the invention provides improved bipolar devices in a process which also provides complementary metal-oxide (CMOS) semiconductor devices and a process for their fabrication.
Bipolar and CMOS devices and their fabrication have been well known for many years. Many techniques have been used to reduce the size of a bipolar transistor and decrease the number of steps required to fabricate the bipolar transistor. For example, bipolar transistors are generally fabricated with the emitter, base, and collector formed in a vertical rather than horizontal sequence. While this generally decreases the size of a bipolar transistor, more steps and space are generally required to provide electrical contacts to each of the elements of the bipolar transistor. In particular, field oxide regions between the base and collector of such transistors presently increase the area of such transistor substantially.
Recently, the advantages of bipolar and CMOS devices have been beneficially incorporated into circuits using both types of devices on a single substrate. Circuits which incorporate both bipolar and CMOS devices have come to be known as "BiCMOS." BiCMOS devices offer the advantages of the high packing density and low power consumption of CMOS devices, as well as the high speed of bipolar devices. However, techniques used to reduce the size of the bipolar transistor and decrease the number of steps required to fabricate the bipolar transistor are many times incompatible or difficult to use with the fabricating of a BiCMOS device. One BiCMOS device and process for fabrication thereof is described in U.S. Pat. No. 4,764,480 (Vora), assigned to the assignee of the present invention and incorporated herein by reference for all purposes.
From the above it is seen that improved bipolar or BiCMOS devices and method of fabrication thereof is desired not only to provide devices with improved performance and reduced size, but also to provide devices which can be fabricated more quickly and economically.